[Gdal-dev] img format resizing
list67 at netscape.net
list67 at netscape.net
Fri Apr 2 14:08:52 EST 2004
Frank Warmerdam <warmerdam at pobox.com> wrote:
>list67 at netscape.net wrote:
>> Hello.
>>
>> I have a possible bug to report.
>>
>> I have a .img file. When I run:
>> gdalwarp -rb -of HFA -ot Byte -wm 512 -ts 1487 2899 ./beforeResize.img ./afterResize.img
>> the afterResize.img file is upside down. Does anyone know if there is
> > something about the above command that should be changed?
>
>Mike,
>
>My guess is that your image has no georeferencing so the source
>image coordinate system "y" is increasing as you move from the top
>to the bottom, as opposed to the "y" decreasing from top to bottom
>as would occur in common projected or geographic coordinate systems.
>
>The warper will generally get ungeoreferenced images upside down I expect,
>though I haven't tried this myself.
>
>....
>
>Hmm, I just tried it, and gdalwarp seems to error out if the is
>no georeferencing (which is good).
>
>Could you provide a gdalinfo report on the input file?
Frank,
Here are the gdalinfo reports for the before and after resizing img files:
gdalinfo ./beforeResize.img
Driver: HFA/Erdas Imagine Images (.img)
Size is 1487, 2900
Coordinate System is:
LOCAL_CS["Unknown",
UNIT["meters",1]]
Origin = (0.000000,0.000000)
Pixel Size = (0.00010000,0.00010000)
Corner Coordinates:
Upper Left ( 0.0000000, 0.0000000)
Lower Left ( 0.0000000, 0.2900000)
Upper Right ( 0.1487000, 0.0000000)
Lower Right ( 0.1487000, 0.2900000)
Center ( 0.0743500, 0.1450000)
Band 1 Block=64x64 Type=Byte, ColorInterp=Undefined
Band 2 Block=64x64 Type=Byte, ColorInterp=Undefined
Band 3 Block=64x64 Type=Byte, ColorInterp=Undefined
Band 4 Block=64x64 Type=Byte, ColorInterp=Undefined
gdalinfo ./afterResize.img
Driver: HFA/Erdas Imagine Images (.img)
Size is 1487, 2899
Coordinate System is:
LOCAL_CS["Unknown",
UNIT["meters",1]]
Origin = (0.000000,0.290000)
Pixel Size = (0.00010000,-0.00010003)
Corner Coordinates:
Upper Left ( 0.0000000, 0.2900000)
Lower Left ( 0.0000000, 0.0000000)
Upper Right ( 0.1487000, 0.2900000)
Lower Right ( 0.1487000, 0.0000000)
Center ( 0.0743500, 0.1450000)
Band 1 Block=64x64 Type=Byte, ColorInterp=Undefined
Band 2 Block=64x64 Type=Byte, ColorInterp=Undefined
Band 3 Block=64x64 Type=Byte, ColorInterp=Undefined
Band 4 Block=64x64 Type=Byte, ColorInterp=Undefined
Do you know of anything I can do to prevent the upside downness?
>> I'm using a cvs version of gdal that was updated today. The
> > beforeResize.img file is about 4.5 MB when gzipped.
>>
>> Also, the reason I'm using the .img format is that I have a program
> > that needs to be able to work with large image files (36GB is the max size
> > so far). The geotiff format has the file size limit. The .img format seems
> > to get unexpectedly large when making modifications to the file. I don't
> > have any test results to back this up. Can anyone recommend one of the
> > other image formats that are suitable for large images files?
>
>What exactly do you mean by "making modifications to the file"? Are you
>dynamically re-write image data after the creation pass? While this should
>- in theory - work, it isn't a path that is well tested. There might well
>be a bug. Please provide some more detail on what you are doing and what
>is going wrong and I might be able to figure out whats happening.
An approximately 36GB img file was reprojected with gdalwarp from something like the following coordinate system:
<SRS>PROJCS["unnamed",GEOGCS["NAD83",DATUM["North_American_Datum_1983",SPHEROID["GRS 1980",6378137,298.2572221010042,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6269"]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4269"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-117],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["unknown",1],AUTHORITY["EPSG","26911"]]</SRS>
using something like -t_srs "+proj=longlat +ellps=WGS84 +datum=WGS84". After this reprojection I think (I had to delete the file to free up space) that the new .img file was approximately 60 GB. Maybe I just wasn't expecting there to be such a difference in file size. After reprojecting, a program added a alpha layer to the .img file. This made the file approximately 90GB. That increase in file size was expected. And finally there was a resize which resulted in a 122 GB .img file. So I guess that it was just the size after reprojection that I wasn't expecting.
Thanks for your help.
Mike
>Best regards,
>--
>---------------------------------------+--------------------------------------
>I set the clouds in motion - turn up | Frank Warmerdam, warmerdam at pobox.com
>light and sound - activate the windows | http://pobox.com/~warmerdam
>and watch the world go round - Rush | Geospatial Programmer for Rent
>
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